High-voltage devices are commonly used in integrated circuits, and may be used in input/output (IO) circuits, memory circuits, and the like. FIG. 1A illustrates a top view of a conventional high-voltage bipolar junction transistor (BJT). FIG. 1B illustrates a cross-sectional view of the structure as shown in FIG. 1A, wherein the cross-sectional view is taken along a plane crossing line 1B-1B. The BJT includes emitter E, collector C, and base contact B. Emitter E and collector C are of n-type, while base contact B is of p-type. Base contact B and the underlying p-well form the base of the BJT. Each of base contact B and collector C forms a ring encircling emitter E. Shallow trench isolation (STI) regions laterally space collector C apart from base contact B, and space emitter E apart from base contact B, so that a high voltage can be applied between collector C and emitter E.
Referring to FIG. 1B, collector C includes a heavily doped n-type region (N+) and a high-voltage n-well (HVNW), each forming a ring, and an n-type buried layer (NBL) underlying and connected to the HVNW. During the operation of the BJT, electrons may be injected into collector C from emitter E through paths denoted using arrows 110 and 112. Arrows 110 indicate lateral electron-injection paths, while arrows 112 indicate vertical electron-injection paths. It is noted that emitter E is laterally spaced apart from the HVNW by two STI regions and base contact B, and hence the lateral electron-injection path is long. Accordingly, the lateral electron-injection effect is weak, and the current gain of the BJT is mainly contributed to by the vertical electron-injection path (denoted by arrows 112).
Due to the lack of lateral electron-injection effect, the current gain of the BJT as shown in FIGS. 1A and 1B is low. In addition, the chip area usage of the BJT is not efficient. The BJT may occupy a chip area of 10 μm×10 μm. What is needed, therefore, is a structure for overcoming the above-described shortcomings in the prior art.